1. Field of the Invention
This invention relates to an improved assembly for producing flat printing plates; and more particularly to an assembly of the character described wherein the resin-supporting glass plate is structurally reinforced so as to maintain its planar condition in the assembly without retarding light transmission through the glass plate.
2. Description of the Art
An assembly for producing printing plates by selectively cross-linking a photo-polymerizable resin layer typically includes an upper fixture assembly having an upper UV light bank, and a lower fixture assembly containing a lower UV light bank. Both assemblies are provided with glass plates, which are brought together when the resin layer is processed. The resin layer is cast on a transparent sheet, which is positioned on the lower glass plate, and the resin layer may be smoothed and evened by means of a doctor blade, which passes over the resin layer. After the smoothing operation, the upper fixture is properly positioned and the light banks are activated so as to selectively cross-link the resin layer so as to form the printing plate. The selective cross-linking is accomplished by means of a photo negative of the pattern desired for the printing plate. The lower UV light bank is directed against the lower surface of the resin layer through the negative. The upper UV light bank is directed against the upper surface of the resin layer so as to form a cross linked floor portion of the printing plate. Excess liquid resin which is not cross linked in the process is removed from the cross linked printing plate.
The aforesaid assembly can be used to produce relatively large area printing plates, but in order to maximize printing plate and print image quality, the lower glass plate must be maintained as flat as possible. The larger the printing plate, the heavier the resin layer that is deposited on the lower glass plate, and the greater the tendency of the lower glass plate to bow downwardly at its center since it is only supported on its edges. The use of a doctor blade also increases bending of the lower glass plate, which results in a thicker resin layer at the center of the lower glass plate. The net result is a resin layer which may not be flat, and which may have a thicker central portion. It would be desirable to be able to provide an auxiliary support for the lower glass plate so as to maintain the flatness of the lower glass plate during production of any size printing plate, and also to allow the production of larger printing plates than are presently feasible.